1. Field of Invention
The invention relates to a method for precision cutting of soluble scintillator materials. More specifically, the invention relates to a method for dicing, slitting, slotting, and segmenting soluble scintillator materials with liquid-wetted filaments.
2. Description of the Related Art
Prior art devices are well known for detecting the distribution of gamma-rays transmitted or emitted through objects to study the compositions or functions of the objects. The devices utilize scintillator crystals with techniques referred to as Emission Computed Tomography, which includes Single Photon Emission Computed Tomography (SPECT), that uses radiotracers which emit gamma-rays but do not emit positrons, and Positron Emission Tomography (PET), that uses radiotracers which emit positrons. The PET technique can determine, in-vivo, biochemical functions, on the injection of biochemical analog radiotracer molecules that emit positrons in a living body. The positrons annihilate with surrounding electrons in the subject body to produce a pair of gamma-rays, with detection of the gamma-rays by two opposed scintillator detectors allowing for the determination of the location and direction in space of a trajectory line defined by the trajectories of the gamma-rays. Tomographic reconstruction is then used to superpose the numerous trajectory lines obtained by surveying the subject with an array of scintillator detectors to image the distribution of radiotracer molecules in the living body.
Emission Computed Tomography systems employ a variety of geometric configurations of scintillator crystals in the gamma-ray detectors. The choice of a configuration is typically dictated by the manufacturer's desired system performance and cost. The detector design must be capable of providing accurate estimates of gamma-ray energy, position coordinates, and in the case of PET, coincidence time intervals to reconstruct an image of the distribution of the radiotracer for in vivo studies. Therefore, the detector design can require the cutting, dicing, shaping, slitting, slotting, and otherwise segmenting of scintillator crystals into a multitude of shapes, either rectangular or cylindrical, having side cuts, end cuts, slits and/or notches partially through the crystals.
Prior art systems for cutting and shaping scintillator crystals include metal band saws to cut alkali-halide scintillator crystals. Band saws create straight cuts with wide (0.030 inches to 0.060 inches) kerfs. The cutting action of the metal teeth create chipping during the onset, middle, and termination of the cut. In addition, metal teeth create sharp and/or jagged edges along a kerf that chip and may break away during use during the crystalline orientation of the scintillator materials. The tendency of jagged edges to break away leads to ease of cleavage along a crystallographic plane, producing scrap scintillator crystals or crystal materials that are unusable for precise determination of gamma-ray or positron energy and position of the trajectory of the gamma-rays. Use of metal band saws or slotting mill cutters create an edge break out that leads to a major source of scrap, unusable scintillator materials. An edge break out is the fracturing of the crystal that occurs as the saw blade is about to break out of the sawn kerf, with parting of the scintillator crystal into two pieces. The thin remaining unsawed piece can break off prematurely, with jagged edges rather than cleanly cut edges. Crystals composed of thallium doped sodium iodide (NaI(Tl)) are especially prone to chipping as NaI(Tl) edges are best chamfered or radiused to minimize chipping. An improved method of cutting and dicing scintillator crystals is needed that provides narrow width, straight kerfs, and gently radiused corners for each kerf cut by the method of cutting.
The SPECT detector systems utilize NaI(Tl) as the scintillator material. These systems can use large continuous slabs of NaI(Tl) optically coupled to a continuous light guide. The exception to continuous NaI(Tl) slab detector systems for SPECT imaging was disclosed by Govaert in U.S. Pat. No. 4,267,452. This detector system is unique as a SPECT detector in that it is segmented. The segmentation of the NaI(Tl) is similar to PET block detector designs which use an active light guide. (For clarification, detector light guides are of two general types: non-active light guides are composed of optical materials other than the scintillator; active light guides are composed of scintillator materials.) The segmentation of the scintillator materials results in a block of NaI(Tl) that is subdivided into elements that share a common light guide of active scintillator material, in other words the NaI(Tl) is not cut all the way through. A precise cutting method is needed to cut numerous kerfs and/or to dice, slot, scintillator material into subdivided scintillator elements and to produce precise partial cuts in scintillator elements that do not lead to breakage and segmentation of scintillator materials during use.
The prior art cutting methods of utilizing string saws wetted with water suffered from the drawback that generally rough cuts are possible while utilizing a water-wetted string saw. The cutting strings of the prior art are typically greater than 1.0 mm in thickness. The cut surfaces of the water-soluble scintillator (NaI(Tl)) form a white, surface, water-induced hydrate (NaI.2H.sub.2 0) that must be ground away with additional cutting or finishing operations to mechanically remove the surface hydrate. NaI(TI) is extremely hygroscopic and quickly forms a white hydrate on the kerf edges of the cut. The presence of the water-induced hydrate is undesirable because the surface coating prevents the escape of scintillator light through the hydrated scintillator surface. Additional cutting or finishing operations do not lead to precise cuts, and require additional preparation time for finishing of the scintillator materials.
Therefore, it is an object of the present invention to provide a method for precision cutting of soluble scintillator materials to precise configurations.
It is another object of the present invention to provide a method for precision cutting, dicing, slitting, slotting, and otherwise segmenting of soluble scintillator materials with a organic solvent wetted moving thin filament.
It is another object of the present invention to provide a method for precision cutting, dicing, slitting, slotting, and otherwise segmenting of soluble scintillator materials utilizing organic solvents to wet a moving thin filament to eliminate water induced hydrates on the cut surfaces of the scintillator materials.
It is another object of the present invention to provide a method for precision cutting, dicing, slitting, slotting, and otherwise segmenting of soluble scintillator materials with a plurality of organic solvent wetted moving thin filaments to increase production rates.